Roof 6: Insulation and Soffits

You order insulation by the square foot. Measure the area you need covered and divide it up into the square footage on each bundle. Each bundle is different depending on the R-value (thickness) and width between studs - 15" or 23". Check out the R-value needed in your area for walls, floors and ceilings. Your building supply dealer should know that.

You should wear a dust mask while installing. Install the batts snug to the sides of the studs or joists, flush with the warm side of the room. Don't jamb it in tight, make sure nothing sticks out over the face of the studs. Apply acoustical caulking to the joint of the floor and the bottom plate of the wall. When installing the polyethylene vapour barrier, bed the poly in this caulking to give a good seal at the bottom and wrap the vapour barrier around the top onto the ceiling. This is a special 6 mil poly used specifically for vapour barrier.

Perforated aluminum or vinyl soffit along the eaves is cut into short pieces along the length of the sheets. A J-molding is nailed to the underside of the rafter or truss trim, against the back of the facia board or gutter. On the wall side is installed a 1x2 with its bottom edge level with the bottom of the trim board. Notice that the aluminum soffit has a tongue on one side and a groove on the other which will snap into each other. Start off at the corner of the house, inserting the soffit into the J-mold and lift it up against the 1x2 and staple or nail it in position. The soffit is usually installed prior to the siding, so the siding acts as a finish under the soffit. If the soffit is put on after the siding then install a trim piece under the soffit on top of the siding. Another way of installing the soffit is to put in an F-molding, if available or a J-molding against the wall in place of the 1x2. This method requires that the soffit panels are slid along the J-mold tracks instead of lifting the panel up against the 1x2. Make sure the panels are cut about 1/4" short to allow for expansion and contraction.

Your source for building tips, woodworking & furniture plans, house plans and building advice directly from Dave...

Hi, I'm Dave Osborne. With over 50 years experience as a journeyman carpenter, foreman and contractor in heavy construction I enjoyed working with apprentices and sharing the tricks of the trade that others shared with me. Now I get emails from Members all over the world and we include many of my answers in our Free Monthly Newsletters. Some of my answers include drawings and instructions specific to a project, but may also answer your questions. I use correct construction terminology, so you can confidently inform your building supply dealers or contractors exactly what you need.